1. Field of the Invention
The present invention relates generally to methods of processing electron gas discharge tubing commonly referred to as "neon tubing" or simply "neon," irrespective of the fill gas used for illumination.
More particularly, the present invention relates to a system and method for closely monitoring, recording, or analyzing the neon processing manufacturing parameters in order to correctly and consistently fabricate reliable luminous neon tubing. In addition, the invention is directed to regulating the neon processing parameters to insure conformance with predetermined manufacturing specifications, and allow the manufacturer of the luminous neon tubing to retain fabrication data and information for a particular piece of neon throughout the duration of its useful life.
2. Description of the Related Art
The neon fabrication industry has developed over the years through trial and error in conjunction with an apprentice/journeyman training system. The production of electron gas discharge tubing is often thought of as an art form. In reality, neon processing involves a complex set of variables which must be carefully balanced and regulated to achieve the desired effect within an anticipated environmental setting.
Some of the critical manufacturing parameters include: glass tube length and diameter, ambient operating temperature, gas pressure, mercury vapor pressure, the resident level of impurities from the glass/electrodes or fill gas, current, voltage, electrode composition, fill gas selection, and electrode processing, to name a few. All such parameters affect the final appearance and performance of a neon tube.
Until now, the resultant state of the neon art, therefore, is based on a tremendous amount of conjecture, opinion, and other subjective factors, thereby rendering the consistency of producing reliable high quality neon signage a near impossibility.
Some industry officials have lamented that if five different neon manufacturers were asked about the source or cause of neon failures, it is likely that five different answers would follow. Consequently, there are many examples of bad or failed neon within the sign industry or otherwise on display in public.
Within the last decade, sophisticated instrumentation, such as highly accurate vacuum gauges, thermocouples, and other instruments have been developed to provide much tighter control over the inherent measurable error associated with the processing of neon tubing, including during the bombarding process described below.
In short, the manufacture of luminous tubing utilizes the principles of quantum theory physics to excite the electrons within a low pressure gas by means of a high voltage, low amperage current. Once excited, the gas will emit energy in the form of visible light, ultraviolet radiation, and heat.
The resultant visible light assumes a color characteristic of the individual gas used. Neon gas, for example, produces a red hue while mercury vapor provides a blue/white light. By using additional phosphor coatings inside the glass tubing, or by actually using colored glass, a wide variety of colors can be produced.
Since sufficient mercury vapor pressure is difficult to maintain at ambient temperatures, argon gas is used as a carrier gas to enable the tube to strike an electrical arc between its electrodes. Once the arc is struck, the elevating temperature of the tube increases the vaporization of the mercury, improving the operation of the tube.
Functional electron gas discharge tubing begins with hollow glass tubing. Typically, glass manufacturers ship glass sealed in plastic bags which contain a desiccant. Once opened, boxes of glass tubing should be and are typically stored in a fashion designed to minimize exposure of the tubing to humidity and moisture moisture. At a minimum, the plastic bag should be resealed immediately after the removal of glass for fabrication.
As alluded to above, the glass tubing can initially be clear, coated, colored lead or soda glass as specified by consumer requirements. The diameter of the glass is usually selected to be as large as possible for the particular application. The glass tubing should be free of any accumulation of dust, dirt, and moisture.
The tubing is typically fabricated to conform to an intended design or shape. It is generally understood in the industry that the diameter of the glass should not change by more than ten percent (.+-.10%) when the tubing is bent. All bends should exhibit minimal flatness, and pinching is not acceptable. Glass should be handled and processed so as to ensure proper annealing of the tube.
After the tubing has been bent, welded, shaped, and annealed, the electrodes are welded to each end of the tubing. Due to differences in emission coatings and construction, procedures may vary between suppliers and among different products from the same source. Electrodes will be sized to match glass tubing diameter and intended operating current requirements. The electrode shell must be centered in the glass casing.
The tube is then "tubulated" with a length of slender glass tubing to provide a means for ingress and egress of gases and air. The tabulation is the means to connect the glass tubing to the processing manifold. After the tubing is tubulated, the tubing is slightly evacuated to check for airtightness.
It is also generally understood in the industry that glass tubing should be bombarded the same day it is fabricated, and the glass tubing should be filled with the fill gas and the electrodes energized to test the tube performance. Bombardment processes are classified as open stopcock or closed stopcock, depending on the manner in which the vacuum is applied during, or immediately after, processing of the electrodes.
Bombardment consists of a series of steps which reduce gas pressure within the glass tube to the point that an electric arc can be struck between the electrodes. The amount of the current is controlled so that the glass tube heats to a predetermined processing temperature which is selected to release impurities from within the glass walls which would otherwise be released during normal tube operations. This temperature is usually in the range of 200.degree.-225.degree. C.
If the glass tubing is coated glass, it is processed to an extremely high heat prior to coating, thereby removing many of the impurities within the tubing prior to its delivery to the neon shop. Clear glass which has not been processed in this manner and must be heated ten to fifteen degrees (10.degree.-15.degree.) hotter than coated glass during bombardment to ensure removal of the impurities.
Coated tubes may experience a breakdown of the phosphors and damage to the tube if the glass is processed at too high a temperature. Careful, closely monitored processing in accordance with the present invention is recommended.
The electrodes are also heated in order to convert the emitter material and release still more impurities. After the glass has been heated to the predetermined temperature, the current to the electrodes is increased until they glow "cherry red". In the industry, "cherry red" is a subjective state and is an inherent source of processing error between one piece of neon to the next.
Overheating or underheating of the electrodes is believed to contribute to inconsistent neon tubing life. Closely monitoring the actual electrode temperature would enable the manufacturer of the tubing to stay within the prescribed electrode temperature ranges of a particular electrode manufacturer, thus minimizing one source of manufacturing error.
The impurities are further removed by establishing a vacuum within the tube, after the current source is disconnected from the electrodes. The glass tubing is typically evacuated to a range of 1 micron (1.times.10.sup.-3 Torr) vacuum as measured on the manifold is vacuum gauge.
If the current source remained attached and continued to supply current to the electrodes when the vacuum manifold was opened in order to create the vacuum condition within the tube necessary to remove impurities, the current could attempt to travel the path of least resistance, i.e., through the vacuum gauge and damage the gauge. This condition is known as "flashback."
The tube is then cooled and filled with the appropriate gas and sealed. As mentioned above, some electron gas discharge tubing requires an amount of mercury to be added to the tube along with the fill gas. Due to mercury's instability, triple distilled mercury is typically referred to as an industry requirement. Due to its high degree of reactance, mercury should be stored in a sealed glass container and handled in accordance with all EPA and OSHA regulations.
Until now, a system for monitoring, recording, regulating, and storing the manufacturing parameters associated with the production of electron gas discharge tubing, tracking the useful life of a piece of neon and comparing the useful life data by comparing it to the manufacturing parameters, as well as to determine the best methods of manufacturing, among other things, has not been invented.